The present invention relates to a method and a device for automatically engaging an automated emergency descent of an aircraft.
The present invention applies to an aircraft, in particular a transport airplane, provided with an automated emergency descent function. Such a function aims to assist the crew of the aircraft in case of emergency descent or to automatically perform said descent if a depressurization is detected. An emergency descent maneuver consists in bringing the aircraft as rapidly as possible to a safety altitude, generally 10 000 feet (approximately 3000 meters) or to the minimum safety altitude which is a function of the elevation of the terrain.
In effect, following a failure (failure of a system or a leak from the cabin), it may be that the pressurization of the aircraft can no longer supply sufficient oxygenation for the pilots and the passengers and cause the altitude of the cabin to exceed a threshold (generally 14 000 feet) which triggers the releasing of the oxygen masks in the cabin. The crew must then apply an emergency descent, which makes it possible to limit the time of exposure of the passengers and of the crew members to the lack of oxygen.
This automated emergency descent can be initiated (or engaged), either manually by the pilot, or automatically when the crew is unconscious, as described for example in the published U.S. Patent Application 2009/0228161.
It is known that the purpose of the pressurization system of the aircraft is to maintain the cabin of the aircraft at an altitude compatible with human life by managing the pressure of the cabin. Thus, when the altitude of the aircraft increases during the climb, the atmospheric pressure decreases, this decrease in the atmospheric pressure being compensated by the pressurization system which adjusts the cabin pressure. When the aircraft is cruising, the cabin is maintained at the pressure adopted during the climb, so the cabin pressure allows the passengers and the crew members to breathe normally.
Furthermore, during the descent, the altitude of the aircraft decreases and the atmospheric pressure increases. The pressurization system adapts the cabin pressure to the height of the destination airport. So, when the aircraft arrives on the ground, the cabin pressure is equal to the atmospheric pressure.
The automatic engagement of the emergency descent function is based mainly on a criterion related to an altitude equivalent to the cabin pressure. Generally, if the altitude reached by the cabin (this altitude is representative of a pressure value relative to the pressure inside the cabin) exceeds a set threshold of 14 000 feet for 15 seconds, the emergency descent function is automatically engaged.
However, the runway altitude of certain existing airports or airports under construction is close to or greater than this threshold of 14 000 feet.
The automated emergency descent function is therefore engaged if the altitude of the cabin exceeds an engagement threshold. However, this engagement must not occur if the aircraft is close to the ground (in case of approach and of take-off) or if the cabin is deliberately depressurized because of operational constraints such as take-off from or approach to an airport at high altitude.
So, there arises the issue of activation (or of engagement) of the emergency descent function in certain operations, notably on airports at high altitudes.